Earlier reports said radiation levels inside the plant surged to 1,000 times more than normal and a small leak was detected.

Government officials later said the radiation leak was decreasing and the explosion destroyed the exterior walls of the building where the reactor is placed, but not the actual metal housing around the reactor.

"We have confirmed that the walls of this building were what exploded, and it was not the reactor's container that exploded," government spokesperson Yukio Edano said.

But it did little to quell nearby residents' fears.

Japanese authorities are planning to distribute iodine, a treatment to prevent radiation poisoning to nearby residents. Those living within a 12 miles radius of the plant were evacuated.

People at a book store react as the store's ceiling falls in Sendai, northern Japan. Kyodo/AP

While its unclear how much radiation has been or will be released, even a tiny amount of extra radiation can cause long-term cancer rates to rise.

The explosion was triggered after an 8.9-magnitude earthquake and tsunami ripped through Japan. It knocked out the power at the facility, depriving it of its cooling system.

Homes, cars and even a ship were swept out to sea with powerful 33-foot-high waves that left a grim trail of mud and mayhem along the country's east coast - and rippled across the Pacific Ocean to Hawaii, Oregon and California.

Earthquake-triggered tsumanis sweep shores along Iwanuma. Kyodo/AP

The natural disaster paralyzed Tokyo and triggered emergencies for five nuclear reactors at two power plants when their cooling systems failed, forcing the evacuations of nearly 14,000 people.

Residents living nearby the Fukushima Daiichi nuclear facility said the widespread destruction made it difficult to leave.

"Everyone wants to get out of the town. But the roads are terrible," Reiko Takagi said. "It is too dangerous to go anywhere. But we are afraid that winds may change and bring radiation toward us."